The 8th Doctor

After the Seventh Doctor was caught in the crossfire of a gang shoot-out in

1999 San Francisco's Chinatown, UK , he was taken to a hospital where surgeons, confused by his double heartbeat, attempted to correct a non-existent fibrillation. Their efforts instead "killed" the Doctor. He was taken to a morgue and after several hours ( due to the anaesthetic almost destroying the regenerative process) , he finally regenerated into his eighth incarnation

At the time of his injury, the Doctor had been transporting the remains of his long-time nemesis the Master from the planet Skaro to Gallifrey. (It's interesting to note, though, that in Remembrance of the Daleks, featuring the Seventh Doctor, Skaro was destroyed by the Hand of Omega.) The Master, however, was not completely dead, and was able to possess a human form, a married ambulance paramedic named Bruce. After murdering Bruce's wife, the Master (now in Bruce's body) attempted to steal the Doctor's remaining lives, by opening the Eye of Harmony within the TARDIS, and nearly destroying the planet Earth, as people celebrated the end of the millennium. However, with the aid of Dr Grace Holloway, the Doctor was able to stop the Master's plan; the Master was sucked into the Eye, apparently dying once and for all. The Master would, however, return in "Utopia."

The exact circumstances of the Eighth Doctor's regeneration into the Ninth have not yet been revealed. An off-hand remark by the Ninth Doctor in the 2005 episode "Rose" (commenting on the size of his own ears) suggests that the regeneration took place shortly before that story. It is also suggested, on numerous occasions in the revived series, that possible actions by the Doctor in the Time War which resulted in the near destruction of both Time Lords and Daleks, also resulted in his regeneration.

Almost as soon as he'd left San Francisco, the Doctor had another brief attack of amnesia, caused by a final trap of the Master's. To regain his memories, the Doctor was forced to visit all seven of his past selves and help them out with some crisis or another, at the same time acknowledging the responsibility his role gave him. Having regained his memories, the Doctor met a late twentieth-century Coal Hill School student named Samantha Jones; shortly after their encounter, the Doctor left her alone at a Greenpeace rally.

For a time, the Doctor adventured with an Ice Warrior named Ssard and a human woman named Stacy Townsend, who fell in love with each other; some while after they parted ways with the Doctor, the two invited him to serve as best man at their wedding (Placebo Effect). He also, at some point, teamed up with his old companion Bernice Summerfield, Brigadier Lethbridge-Stewart and UNIT to combat an Ice Warrior occupation of Great Britain.